Stock-Based Compensation (Details) (USD $)	6 Months Ended
	Jan. 31, 2012 Y	Jan. 31, 2011 Y
Performance Based Options [Member]
Stock Option Assumptions
Expected term (in years)	6.57	6.57
Expected volatility	39.21%	39.39%
Expected dividend yield	1.99%	1.96%
Risk-free interest rate	2.05%	2.35%
Weighted-average market value of underlying stock at grant date	$ 29.55	$ 28.43
Weighted average exercise price	$ 29.55	$ 28.35
Weighted-average fair value of options granted during the period	$ 10.01	$ 9.87
Service Based Options [Member]
Stock Option Assumptions
Expected term (in years)	5.89	5.92
Expected volatility	39.40%	40.22%
Expected dividend yield	2.07%	1.94%
Risk-free interest rate	1.16%	1.65%
Weighted-average market value of underlying stock at grant date	$ 27.00	$ 29.09
Weighted average exercise price	$ 27.00	$ 29.09
Weighted-average fair value of options granted during the period	$ 8.37	$ 9.58